2000 transit times and declination charts

Contents

Overview

This page describes charts for the year 2000 which can be downloaded
in Adobe Acrobat format or as a large GIF. These charts show on one side
of A4, for each day in the year 2000;

The transit time of the Sun and major planets for Northern observers

The declination of the Sun and major planets

These charts enable you to decide on your chances of seeing a given
planet on a given day in 2000. The charts are modelled on those found on
pages A6 and A7 of the Astronomical Almanac, and this page forms
a minor protest at the refusal of my local reference library to stock the
Almanac. These charts provide enough detail for most simple planning
exercises, without using any batteries and requiring no mouse clicks. I
believe that they give some insight into the motions of the planets in
the sky, and how the sky works.

In the Northern hemisphere, the sphere of stars seems to revolve around
the Pole Star, in the Northern part of the sky. Stars near Polaris never
rise or set, but as you look further to the south, you will find stars
which rise in the east and set in the west. Imagine a line on the sky drawn
from the South pole, through the point directly overhead, to the North
celestial pole. This line is your meridian. The transit time
for a star or other celestial object is the time the object crosses your
meridian south of the celestial equator. This transit time also corresponds
to the time when the object is highest in the sky for Northern observers,
and is also known as culmination, or upper culmination in
the case of a star which does not rise or set.

Some stars do not stay in the same position on the Celestial Sphere.
These wanderers are the planets, and their transit times will change from
day to day. A chart of the transit times for the Sun, Mercury, Venus, Mars,
Jupiter and Saturn will give you a good idea of the observability of these
planets, and which constellation they are in on a given day of the year.

Download or print the charts

The charts were produced in Microsoft Excel, and are available here
as an Adobe Acrobat file (for which you need a copy of the Adobe
Acrobat reader) and as large GIF file. The Adobe versions provide much
better print quality, and the whole point of these graphs is to print them
onto paper.

To print the Adobe format version, some browsers use the Adobe Acrobat
reader as a plug-in, so following the link will load the reader. In this
case, just hit print. With older browsers, you will need to save the Adobe
Acrobat file to your computer, and then load it into the reader to print
the file.

The Adobe Acrobat file was generated using the freeware GhostScript
and an Adobe Acrobat PostScript printer driver. If you have any problems
rendering the file, I would like to hear from you.

Using the charts

The charts use day numbers in 2000, a leap year, so use the table below
to find the number of any day.

Jan 0 Jul 182
Feb 31 Aug 213
Mar 60 Sep 244
Apr 91 Oct 274
May 121 Nov 305
Jun 152 Dec 335
To find the day number of any date in 2000, just add the date to the
number of days before the month given above. eg, May 26th 2000 is day
number 121 + 26 = 147

To find the transit time of a given planet or the Sun, you just

use the table above to find the day in 2000

put a ruler parallel to the time axis at the day number on the date
axis (horzontal axis)

identify the point at which the ruler crosses the transit time line
for the planet

read off the corresponding time on the time axis (vertical axis)

add 4 minutes for every degree west of the meridian for your time zone,
and subtract 4 minutes for every degree east

and add an hour for daylight saving if needed.

The corrections in step 5 and 6 depend only on your location - you can
work out the correction and write the figure on the charts.

Reading off the declination is very similar, except there is no need
to correct for local time. Once you have the declination, you can easily
work out the altitude of the object at transit - if you know your geographical
latitude.

Take 90 less your latitude

Add the declination if positive

Subtract the declination if negative

This altitude at transit is the highest the planet gets during
the day

In practice, I tend to work to the nearest 10 day period on the days
axis, and I tend to regard each major division as a month. This leads to
a worst case error of 5 days at the end of the year - not too dramatic
for most of the planets (but possibly important for fast moving Mercury).

Example: Transit time and declination of Venus

Below, I find the transit of Venus on 13th March 2000 (day 73).

I locate 73 days on the horizontal axis

I draw a line up to the Venus curve

I continue a horizontal line to the time axis

I read off 1050 roughly as the local time of transit from the graph
above,

I am 1 degree 55 minutes West of my zone meridian so I add 8 minutes,
to give roughly 1058 as the time of transit in zone time.

This puts Venus 57 minutes ahead of the Sun, so Venus will still be
visible in the mornings just before Sun rise, but the planet will soon
be lost in the dawn glow.

The demonstration version of SkyMap
Pro gives 1052 for the transit, within 6 minutes of my estimated time.

I estimate the declination for Venus on the same day to be -12 degrees:

As I live at a latitude of 52.5 North, I expect to find Venus at

90 - 52.5 = 37.5 deg

37.5 - 12 deg = 25.5 deg

at the time of transit. This is not much use for Venus so near the Sun,
but for planets further from the Sun, you can get a good idea of where
to find them in the night sky. SkymapPro gives -12 deg 29 arcmin for the
declination of Venus, and 25 deg 24 arcmin for its altitude at the time
of transit.

You may have noticed that Venus and Mercury are close in the sky around
March 13 - 16.

Interpreting patterns

A look at the Transit chart will convince you of the following general
principles

Planets are hard to see when they are close to the Sun, so if a planet
transits within 45 min of the Sun, you won't be able to see it

Planets which transit after the Sun will also be above the horizon
after sunset, and will be 'evening objects'.

Planets which transit before the Sun will also rise before the
Sun, and will be 'morning objects'.

Planets which transit around 24 hrs or 0 hrs (which are the same -
imagine the transit time chart to be a horizontal cylinder) will be visible
all night.